Commercial establishments use large exhaust hoods over cooking surfaces, e.g. a fry plate, to remove the cooking fumes. For effective fume removal, it is necessary that large volumes of air be exhausted through these ducts and that a corresponding amount of fresh, exterior air enter the building at other locations. For example, with a canopy type hood, the National Fire Protection Association Code (No. 96, Appendix A) specifies that the exhaust air in cubic feet per minute should be between 100 and 150 times the entrance area (front, sides, etc.) of the hood in square feet. Since this same amount of air must necessarily be drawn in from the outside, the result is that there is a correspondingly increased load on the heating and/or air conditioning system of the building. Of course, this requires additional energy and is a corresponding expense to the operator of the business.
In an effort to alleviate this expense, various forms of "direct make-up air hoods" have been devised. These hoods have provision for drawing in air directly into the hood from the outside, and thus that air is not acted upon by the heating/air conditioning system of the building. This direct make-up air is then directed in streams within the hood in a manner intended to entrain the cooking fumes for removal through the hood. However, the codes applicable to exhaust hoods invariably require that a direct make-up air hood exhaust a greater quantity of air than would otherwise be the case. Thus, to a significant extent, the use of a direct air make-up hood is self-defeating because larger exhaust fans are then required, the larger exhaust fan being more expensive and using more energy. Direct make-up air hoods have the further disadvantage that, because of the larger volumes of air being handled, higher air velocities generally result. In general, high velocities usually cause turbulence in the capture and entrainment air streams, thus greatly reducing the efficiency of the hood for capture and removal of cooking fumes.
The present invention is directed to a method and apparatus for exhausting cooking fumes through a hood, without utilizing direct make-up air as discussed in the preceding paragraph, but more effectively entraining the cooking fumes in the air being exhausted from the building so that the quantity of air being exhausted can be reduced. Obviously, there is an enerby saving and thus a monetary saving to the extent that the heated or air conditioned air removed from the building is diminished. In the present invention, the sheet metal of the hood is so arranged that the air being drawn into the exhaust hood is directed so as to sweep through the space above the cooking surface and thereby more effectively entrain the cooking fumes for removal by that air.
Further objects and advantages will become apparent from the following description and drawing.